In the manufacture of gas-fired furnaces it is now customary to provide some form of corrosion protection for the heat exchangers used therein. One form of corrosion protection involves the use of procelainized heat exchangers. Another form involves the use of aluminized steel heat exchangers.
The steel sheet material used in aluminized heat exchangers may be coated in any conventional manner whereby a coating of aluminum is retained on the surface thereof. Outer coatings of aluminum and aluminum-silicon have been used for this purpose. A thin iron-aluminum alloy layer will normally exist between the outer coating and the steel substrate. Such coatings are normally accomplished by a hot-dip process wherein the sheet steel is dipped into molten aluminum and subsequently rolled. The aluminized steel sheet may also be constructed in other ways such as electroplating, diffusion cladding, vapor deposition, electrophoresis, slurry coating or by flame spraying. In either event the coating of aluminum is left on the surface and is considered to be highly instrumental in establishing the corrosion resistant characteristics attributed to heat exchangers of this construction.